The DPRK does not stamp passports, and there's no way for the ROK to know where you flew to with those Chinese exit stamps. In my (limited) experience, passport inspections at Seoul tend to be cursory at best anyway.

Not to Hijack your threat, but I would encourage anyone considering visiting North Korea to think about how your tourist dollars benefit the regime there. Just a thought.

Also, such travel, if undertaken outside of say an academic exchange, will almost certainly disqualify the traveler from subsequently obtaining a government security clearance anytime soon, if that sort of thing may matter for professional reasons.

The DPRK does not stamp passports, and there's no way for the ROK to know where you flew to with those Chinese exit stamps. In my (limited) experience, passport inspections at Seoul tend to be cursory at best anyway.

That's not entirely true. It depends on where your DPRK visa is issued, oddly. If it's issued from the DPRK embassy in Beijing, it's on a piece of paper and not in your passport. If it's issued by the DPRK embassy in London, however, it's put in your passport. DPRK immigration will stamp your visa, wherever it is.

I was in DPRK in late August and ROK two weeks later. I didn't have any problem getting into ROK and I don't think ROK immigration would have any problem with you having been in DPRK.

As far as security clearances go, as the U.S. doesn't restrict travel or spending by U.S. citizens in DPRK (unlike the policy towards Cuban travel), I don't think traveling to DPRK would necessarily disqualify you from a security clearance (at least that's what I'm counting on).